The main objective of this research is to understand the mechanism of action of morphine and related narcotic analgesics, with special reference to the mechanisms by which they produce tolerance and physical dependence. The development of physical dependence is regarded as an important reason for human addiction to these drugs. As one approach to this problem, the mechanism of action of insulin on the rat diaphragm (and possibly other peripheral tissues) will be studied. Insulin ordinarily stimulates the uptake of glucose by skeletal muscle, but it has been reported that diaphragms isolated from rats which have been chronically treated with morphine are insensitive to this effect of insulin. The addition of morphine to the muscle in vitro restores sensitivity to insulin, i.e., the muscle becomes dependent on morphine for normal function. To determine the reason for this, the effects of insulin on glucose uptake, amino acid uptake, intracellular nucleotides (including both cyclic AMP and cyclic GMP), glycogen synthetase activity, protein synthesis, and the properties of the muscle protein kinase system will be studied before and after chronic treatment with morphine, and in the presence and absence of morphine added in vitro. Other agents known to affect these parameters will also be studied in the presence and absence of morphine. The possible effect of insulin on the formation of a heat-stable protein which inhibits protein kinase activity will also be measured under these conditions. Similar studies on isolated fat cells will be done if fat cells are affected by morphine. As another approach to the problem of morphine action, to be taken simultaneously with the above, specific pharmacologic agents will be used to determine the neurotransmitter(s) involved in the centrally mediated effects of morphine on body temperature (hypothermia in most species, hyperthermia in some). These effects are more easily quantitated than certain of the other central effects of morphine. If tolerance develops to them, and if the neurotransmitter involved can be identified, then we may be able to apply our knowledge of the mechanism of action of morphine in simpler peripheral systems to a better understanding of its central effects.